On 2001.08.17 16:31:43 -0400 Dain Sundstrom wrote:
> Sorry for the confusion. There are two issues here.
>
> ==================================================
>
> Issue1: use of the {fn concat(str1, str2)} style functions.
>
> Solution: use fn style functions as default but have override in xml
> like:
> <concat-function>CONCAT (?1, ?2)</concat-function>
> or some thing simmilar.
Conceivable alternate solution:
Since we are now using resource adapters to wrap the db connections, we
could write resource adapters for each non-compliant db that suitably
rewrites these functions to something the db will accept. Puts the pain
where it belongs.
Having a db - specific wrapper-rar might make ManagedConnectionFactory
configuration a lot simpler too.
>
> ==================================================
>
> Issue 2: IS EMPTY function. How should I map the following ejb-ql query:
>
> SELECT OBJECT(o)
> FROM Order o
> WHERE o.lineItems IS EMPTY
>
> Solution A:
>
> SELECT o.ordernumber
> FROM Order o
> WHERE NOT EXISTS (
> SELECT l.pk
> FROM Order o, LineItem l
> WHERE o.ordernumber = l.ordernumber)
>
> I like this because it does not use an outer join (thanks Dave Smith).
> Does
> it have performance problems?
>
> Solution B:
>
> SELECT o.ordernumber
> FROM Order o LEFT OUTER JOIN LineItem l ON o.ordernumber = l.ordernumber
> WHERE l.ordernumber IS NULL
>
> This would be a major pain to map to all vendors.
>
I think which works better is going to depend on what kind of mistakes are
in the particular db's optimizer. Naively I would expect (A) to be easier
to make fast, but I haven't done comparisons. Go for (A) and see if anyone
complains and what db.
david jencks
>
>
>
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